It is often necessary to test an electrical device commonly referred to as a device under test (“DUT”) in order to identify faults, verify performance, and determine characteristics of the DUT. In electrical systems, numerous test devices and circuits may be connected together to form a system under test (“SUT”) that includes a DUT. In order to test the SUT, these test devices and circuits are calibrated and functional models are created for the DUT using linear signals and inputs. But, the approach of using linear signals and inputs for testing and functional modeling often does not compensate or take into consideration the non-linear input that the DUT may typically experience when used in the real world.
In another approach to calibrating test devices and modeling DUTs for model-based tests, the DUT is excited with white, zero-mean noise that is band-limited to the frequency range of interest. The white, zero-mean noise is then scaled so that the maximum and minimum values of the signal correspond to the maximum and minimum output of the excitation of the digital-to-analog converters or arbitrary waveform generator. The response of the SUT is then measured enabling a functional model of the DUT. This functional model of the DUT may then be used for performance model-based testing as discussed in U.S. Pat. No. 6,850,871, titled “Extraction of Nonlinear Black Box Behavioral Models from Embeddings of Time-Domain Measurements,” and U.S. Pat. No. 6,775,646, titled “Excitation Design and Model Structure for Data Driven Models of Electronic System.”
A problem that exists with the previous approaches to performance model-based testing is that they have Fourier components in their signals and the signals will generally not have an integer number of cycles within the time window of the excitation signal. This reduces model extraction accuracy and is the result of transformations, such as leakage that occurs when the input and output signals are Fourier transformed.
In yet another approach to performance model-based testing, a modulated signal similar to a normal operation signal is applied to the DUT. This signal is typically random so that the DUT is excited over the entire normal frequency and instantaneous power range of normal operation. This is an improvement over linear excitation or white noise excitation, but is impractical for CDMA type modulated signals. CDMA type modulation consists of a pseudo-random sequence that is mixed and filtered. This is a random signal with components in the power spectral density at all frequencies and hence the leakage cannot be systematically controlled.
Furthermore, normal modulation signals used in the CDMA protocol, such as the 5 Mhz channel signal, covers only a limited bandwidth. A typical normal CDMA operation signal covers a 5 Mhz channel and requires multiple experiments to cover the wideband frequency response of the devices since typical performance metrics are measured from signals outside of the CDMA information channel. For example, a 100 Mhz frequency band may be required to test the out-of-channel harmonic response (e.g. IP2, IP3 and higher order nonlinear harmonic responses) and this 100 Mhz frequency band requires additional tests (in this example, at least 20 additional tests).
Therefore, there is a need for an approach to provide a SUT with an excitation signal for model-based testing, that results in a model with substantially less model bias, where model bias results in less accurate predictions of test metrics.